I once bought some Wooly Nylon serger thread...for my serger. It is a super stretchy thread that is made for knit fabrics. For things like t shirts & leggings, sweat pants etc.
One day I decided to try it out (on my domestic machine....Not the longarm) on some fmq. I used a knit needle, and loosened the tension a bit. After messing with it for a while (I had to put a spool net on the cone), it was so fun. I had it in several colors, and it added a texture that was so unexpected and cute. After practice & play, I did a whimsical bird & picket fence & flowers wall hanging. It also made cute butterflies & bees.
I don't think I will use serger thread for construction, but it's great for decoration. It works well when couching yarn or ribbon, etc. too.